1. Field of the Invention
The present invention relates to an image processing apparatus which can be used in a recording apparatus such as a color laser beam printer, color LED printer, or the like which forms a multicolor image on the basis of image signals regarding a plurality of color components.
2. Related Background Art
In recent years, the laser beam printer is widely used as an output apparatus of a computer.
For instance, as shown in FIG. 6, a conventional laser beam printer 53 comprises: a printer engine 51 to actually print an image onto a photo sensitive drum on the basis of pixel data; and a printer controller 52 connected to the printer engine 51. The printer controller 52 receives code data which is sent from an external host computer 54 and produces page information consisting of pixel data on the basis of the code data and sequentially sends the pixel data to the printer engine 51. The host computer 54 loads one kind of application software from a floppy disk 55 having a number of kinds of application softwares and actuates a program of the application software. For instance, if a color image process is executed by the application software, the user can produce many multicolor information and store such.
FIGS. 7A and 7B show a construction of a signal processing circuit of the printer controller 52 and the transfer order of signals.
As shown in FIG. 7A, one of an R (red signal 4, a G (green) signal 5, and a B (blue) signal 6 as image signals from the host computer 54 is sequentially selected by a switching control circuit 2. The selected image signals are converted into an M (magenta) signal 8, a C (cyan) signal 9, and a Y (yellow) signal 10 as printing signals by a color conversion processing circuit 3 and are supplied to the printer engine 51. The converted M, C, and Y signals are further compared with signal information to produce a Bk (black) signal (not shown) by a Bk generation circuit 15, so that a Bk printing signal is generated and stored into a page memory 1.
That is, as shown in FIG. 7B, the R signal 4 is converted by the color conversion processing circuit 3 and the M signal 8 is output. After that, the R signal 4 is again selected. Then, the R signal 4 is converted by the color conversion processing circuit 3 and the Y signal 10 is generated. As mentioned above, the R signal 4, G signal 5, and B signal 6 are sequentially selected by the switching control circuit 2 and converted by the color conversion processing circuit 3 and all of the M signal 8, C signal 9, and Y signal 10 are generated. After that, the data in the page memory 1 is generated as a Bk signal 11. The developing order of the image signal at this time is set in a manner such that as shown in FIG. 7B, RGB signals 20 from the host computer 54 are transferred every picture plane (i.e. one frame of a picture) to the color conversion processing circuit 3 six times. That is, the signals are transferred frame-sequentially. In accordance with the transfer of the RGB signals, output signals 21 of Y, M, C, and Bk are transmitted to the printer engine 51 seven times.
As mentioned above, hitherto, by sequentially switching the R, G, and B signals every picture plane and converting into the Y, M, C, and Bk signals and generating, the multicolor image process by a small memory capacity is realized.
However, in the printer controller of the conventional multicolor recording apparatus which receives multicolor image signals from the host apparatus such as a host computer or the like as mentioned above and converts into the printing signals, the image signals from the host apparatus are requested a plurality of times and image process are successively executed instead of using a method whereby all of the image signals from the host apparatus are stored into the buffer memory in a lump and the data contents of the memory are sequentially read out and image processed. Therefore, if a communication error is generated during the transmission or upon reception on the printer side, there is a problem such that a multicolor image which was requested from the host apparatus cannot be formed.
Even if a retransmission is requested in the case where such a communication error was generated, the image data is not always properly received by such a request.
If the image data is printed out in a state in which the image data is insufficient, it is impossible to clearly distinguish whether the printout image is an image which should inherently be transmitted or an image due to the communication error.
On the other hand, assuming that a reproducing process is not executed to a part of the image data due to a communication error, transmission and reception of an image must be again executed from the beginning even for an image such as a picture in which it is sufficient that the outline of the image can be understood, so that a communicating efficiency fairly deteriorates.
Such a problem is important, particularly, in the case of color image communication in which a plurality of color component signals are transmitted and received.
A technique such that a predetermined mark is inserted into an image to be reproduced when a communication error of a black and white image was generated has been disclosed in U.S. Pat. No. 4,814,892. However, the above technique doesn't handle a color image and is still insufficient to solve the problems as mentioned above.